The invention relates to an at least quasi-continuous thrust device using a plurality of hydraulic jacks.
In certain technical applications, more particularly in mining, there is a need to thrust an object or to haul a machine or a support by means of a plurality of jacks. One example of thrusting by means of a plurality of jacks, is the scraping of armoured conveyors along a coal, or other mineral, cutting face, which necessitates a large number of thrust jacks. The moving forward of support piers, either by shifting jacks or by ratchet jacks included in the pier itself, may also be mentioned. Descriptions of such a pier may be found in the Applicant's United States Patent Application Ser. No. 858,064 filed Dec. 6, 1977 now U.S. Pat. No. 4,114,385.
In every application where a plurality of thrust jacks is used, there is a problem of returning to the starting position of the jack which is at the end of its thrust stroke. In practice, this operation necessitates a large number of manual operations which were difficult to co-ordinate. When a jack is at the end of its stroke, it must be reset while the other jack or jacks are locked.
A main object of the invention is to eliminate the manual operations by subordinating the operations to one another, thus permitting a total automation of the thrust.